[PATCH] xfs: Improve scalability of busy extent tracking

[Christoph Hellwig]

Been looking at this a bit and I have a theory:

 - a tid is not actually unique to a xfs_trans structure, if
   we call xfs_trans_dup a single xlog_ticket, and with that the
   tid is re-used by multiple transaction structure.
 - because of that the major semantic change in the version vs
   the previous one is that we now do not force the synchronous
   transaction for the case where we re-used a block in
   the rolled over transaction.

Still not quite sure about the implications of this.